The present invention relates to coupling assemblies for conduits or tubes used to carry fluid (e.g., liquid, air, gas, etc.), and more particularly, to releasable coupling devices by which the tube or conduit inserted into the coupling device may be disengaged and withdrawn therefrom. Such coupling devices are particularly useful in hydraulic or pneumatic equipment for automatic operation, the coupling devices being used to make either joints between two tubes or conduits, or joints between tubes and the pneumatic or hydraulic component part of such equipment.
Releasable coupling devices are generally known in the art. Such known devices generally comprise a coupling member having a bore into which a conduit or tube to be connected or coupled thereto is introduced and held thereinplace by action of gripping teeth of a retaining element which is inserted in the radial gap between the bore and the tube. An unlocking member is generally provided which is adapted to release the gripping action of the teeth. The known devices also generally include a packing ring for sealing the bore and the conduit or tube inserted thereinto to prevent leakage of fluid between the coupling member and the conduit or tube coupled thereto.
In many of the prior art devices, the sealing or packing ring is disposed below the elevation of the gripping fingers, i.e., between the end of the bore at the interior of the coupling member and the end of the gripping fingers. For example, such an arrangement is shown in U.S. Pat. No. 3,909,046 for "Connector For Fluid Conduits, Such as Semi-Rigid Pipes", issued Sept. 30, 1975 to Legris. Since such packing or O-rings normally comprise a hard rubber material, and since the gripping fingers of such devices have serrations or pointed tips which, upon insertion of the tube or conduit, cause the exterior surface of the tube to be scratched or marred, the hard rubber O-rings may not serve to adequately seal and prevent leakage of fluid from the interior of the coupling body around the exterior of the tube, i.e., along the serrated portion of the exterior surface of the tube. In other words, because of the composition of the materials used, an adequate seal may not be provided by the O-ring, since the O-ring may not deform to a sufficient extent to fill the grooves in the outer surface of the tube caused by gripping fingers upon insertion of the tube. It is to be noted that such tubes for these coupling devices are often made of a semi-rigid plastic which is easily marred by the tips of gripping fingers which are generally metallic, such as brass, etc. As can be appreciated, such an arrangement is disadvantageous where it is desired to prevent any leakage. Further, the device of the Legris patent has been found to unexpectedly unlock or release the tube from gripping engagement as a result of vibrations when the fluid pressure is low.
Another prior art coupling assembly is disclosed in U.S. Pat. No. 4,021,062, for "Coupling Assemblies", issued May 3, 1977, to Mariaulle. There, a coupling assembly is adapted to be inserted and cemented in place in a bore of a fitting for coupling a tube to the fitting. The coupling assembly comprises a retaining ring having a plurality of gripping fingers inwardly biased and an unlocking ring between the retaining ring and the conduit or tube to be inserted therethrough. The unlocking ring is operable, on being pushed axially, to spread the gripping teeth of the retaining ring to release the tube or conduit. Two generally different sealing embodiments are disclosed in that patent. One embodiment, like that of the Legris patent, has the sealing O-ring disposed below the gripping fingers, and accordingly, is subject to the same limitations and disadvantages discussed above with respect to Legris--namely, the possibility of not providing a complete and adequate seal since the hard packing ring may be incapable of filling in grooves or serrations on the outer surface of the conduit caused by the gripping fingers upon insertion of the conduit. The other sealing embodiment of the Mariaulle patent discloses the fluid tight packing O-ring being interposed either between the unlocking ring and the gripping fingers or between adjacent halves of the unlocking ring so that the axial unlocking force is transmitted through the packing ring. Accordingly, the axial unlocking force must be greater than is normally necessary to cause unlocking of the gripping fingers since part of the force is dissipated in or absorbed by the non-rigid, deformable packing ring. Thus, this sealing arrangement also is disadvantageous as it is more difficult to cause disengagement of the gripping fingers from the conduit or tube. Furthermore, in the Mariaulle patent, the coupling assembly is relatively more expensive to manufacture since it first requires sub-assembly at the manufacturing location and then a second operation for fixably securing the assembly in a coupling member having the bore. Further, cementing of the coupling assembly into the fitting has been found to be inadequate sealing of the tube.
Turning to another aspect of the prior art, metallic retaining rings for releasable coupling devices which have downwardly depending inwardly biased gripping fingers have generally been manufactured by first forming a cup-shaped member from a metallic plate, such as for example, by drawing or bending of the metal. Then, the bottom of the cup and portions of the side are cut out to define a plurality of gripping fingers depending from a completely closed ring-shaped member. The formed gripping fingers can be biased further inwardly, such as by bending, or, if the cup-shaped member initially has inclined sides, the formed gripping teeth may be sufficiently inclined without further bending to provide inwardly biased gripping fingers. As can be appreciated, there is a substantial amount of waste which results from such prior art manufacturing methods. For example, it has been found that such methods have resulted in waste amounting to 75% of the weight of the metal from which the cup-shaped member is initially formed. This quantity of waste is quite significant, especially when metals such as brass are utilized to manufacture the metallic retaining rings.